Electric machine assembly with reduced rotor post leakage

ABSTRACT

An electric machine assembly includes a rotor formed from one or more magnetically conductive sheets having elongated magnetic flux barriers separated from each other in radial directions that radially extend away from an axis of rotation of the rotor. The magnetic flux barriers are separated from each other by magnetic flux carrier portions of the one or more magnetically conductive sheets. The assembly also includes a non-magnetic post coupled with the magnetic flux carrier portions of the one or more magnetically conductive sheets on opposite sides of at least one of the magnetic flux barriers. The non-magnetic post is elongated in the radial directions from a first magnetic flux carrier portion to a second magnetic flux carrier portion of the magnetic flux carrier portions on the opposite sides of the at least one magnetic flux barrier.

FIELD

The subject matter described herein relates to electric machines, suchas electric motors.

BACKGROUND

Electric machines such as synchronous reluctance and interior permanentmagnet (IPM) machines rely on the flow of magnetic flux in rotors of themachines to generate torque. The rotors include mechanical features(e.g., shapes) which act as magnetic flux guiding channels and otherfeatures that operate as flux barriers. These guiding channels provide asmaller reluctance path along one axis of the machine (e.g., the director d-axis) and the flux barriers provide a greater reluctance path alonganother axis of the machine (e.g., the quadrature or q-axis). Thedifference in reluctance along these different paths and axes providesan overall reluctance torque.

The difference in reluctance is created by the shape and size of theflux guiding channels and flux barriers in the rotor. Due to the speedat which the rotor spins during operation, the flux guiding channels maybe subject to large forces. Posts can extend between the channels andbridges can connect the ends of the channels to provide structuralsupport to the flux guiding channels. But, these posts and bridgesprovide locations for increased flux leakage in the machine. This fluxleakage decreases the power factor and torque density of the machines,and can require increased voltages to be supplied to power the machines.

BRIEF DESCRIPTION

In one embodiment, an electric machine assembly includes a rotor formedfrom one or more conductive sheets having elongated magnetic fluxbarriers separated from each other in radial directions that radiallyextend away from an axis of rotation of the rotor. The magnetic fluxbarriers are separated from each other by magnetic flux carrier portionsof the one or more conductive sheets. The assembly also includes anon-magnetic post coupled with the magnetic flux carrier portions of theone or more conductive sheets on opposite sides of at least one of themagnetic flux barriers. The non-magnetic post is elongated in the radialdirections from a first magnetic flux carrier portion to a secondmagnetic flux carrier portion of the magnetic flux carrier portions onthe opposite sides of the at least one magnetic flux barrier.

In one embodiment, a rotor of an electric machine assembly includesplural conductive sheets laminated with each other. The conductivesheets have elongated magnetic flux barriers separated from each otherin radial directions that radially extend away from an axis of rotationof the rotor. The magnetic flux barriers are separated from each otherby magnetic flux carrier portions of the one or more conductive sheets.The rotor also includes non-magnetic posts coupled with the magneticflux carrier portions of the one or more conductive sheets on oppositesides of at least one of the magnetic flux barriers. The non-magneticposts are elongated in the radial directions from a first magnetic fluxcarrier portion to a second magnetic flux carrier portion of themagnetic flux carrier portions on the opposite sides of each of themagnetic flux barriers.

In one embodiment, a method includes obtaining conductive sheets andforming elongated magnetic flux carrier portions of the conductivesheets by cutting elongated magnetic flux barriers into the conductivesheets. The magnetic flux barriers are cut into the conductive sheetssuch that the magnetic flux barriers are separated from each other inradial directions of the conductive sheets. The method also includesinserting non-magnetic posts into the magnetic flux barriers such thateach of the non-magnetic post is elongated in a different radialdirection of the radial directions from a first magnetic flux carrierportion to a second magnetic flux carrier portion of the magnetic fluxcarrier portions on opposite sides of at least one magnetic fluxbarrier, and forming at least part of a rotor for an electric machineassembly using the conductive sheets having the magnetic flux carrierportions, the non-magnetic posts, and the magnetic flux barriers.

BRIEF DESCRIPTION OF THE DRAWINGS

The present inventive subject matter will be better understood fromreading the following description of non-limiting embodiments, withreference to the attached drawings, wherein below:

FIG. 1 illustrates one example of an electric machine assembly;

FIG. 2 illustrates one example of a segment of a rotor of the machineassembly shown in FIG. 1 having flux carrier portions and flux barrierportions;

FIG. 3 illustrates one embodiment of a segment of a rotor of the machineassembly shown in FIG. 1 having the flux carrier portions and the fluxbarrier portions shown in FIG. 2;

FIG. 4 illustrates examples of airgap torques that are generated byrotation of the rotors shown in FIGS. 2 and 3 with and withoutferromagnetic posts shown in FIG. 2;

FIG. 5 illustrates a front view of a rotor of the electric machineassembly shown in FIG. 1 according to another embodiment;

FIG. 6 illustrates a perspective cut-away view of the segment of therotor shown in FIG. 5 according to one embodiment;

FIG. 7 illustrates a cross-sectional cut-away view of the segment of therotor shown in FIGS. 5 and 6;

FIG. 8 illustrates a front view of a segment of another embodiment of arotor of the machine assembly shown in FIG. 1;

FIG. 9 illustrates a flowchart of one embodiment of a method formanufacturing a rotor of an electric machine assembly; and

FIG. 10 illustrates another embodiment of a rotor of the electricmachine assembly shown in FIG. 1 according to another embodiment.

DETAILED DESCRIPTION

One or more embodiments of the inventive subject matter described hereinrelate to electric machine assemblies that provide for improved torquedensity due at least in part to changes in the features in the machinesthat provide for magnetic flux carrier portions and/or magnetic fluxbarrier portions. The machines can be synchronous reluctance andinterior permanent magnet machines. A stator of the machine can be astator having distributed or concentrated windings. A rotor of themachine includes a laminated stack of electrical sheets (e.g., steelsheets) that are insulated from each other and clamped together. Therotor includes features that operate as magnetic flux guiding channelshaving a lower reluctance along the quadrature or q-axis of the machine,and a higher reluctance along the direct or d-axis of the machine.

The difference in reluctance along the different axes leads to anoverall reluctance torque of the machine. The difference in reluctanceis created by the shape and size of the flux carrier portions and theflux barrier portions of the rotor. In one embodiment of the inventivesubject matter, the ferromagnetic posts that are present in some knownelectric machines are replaced with non-magnetic posts, or posts thatare not formed from a ferromagnetic material and therefore do not allowmagnetic flux to flow through the non-magnetic posts. Removing themagnetic posts from the rotor can reduce the flux leakage that occurs inthe posts of known machines. This can improve the power factor of themachine by increasing the torque density of the machine and/or reducingthe voltage needed to generate the same amount of torque (as a machinewith ferromagnetic posts).

In one embodiment, the non-ferromagnetic posts described herein areformed from one or more dielectric or insulating materials, and are notformed from a dual phase magnetic material. Dual phase magneticmaterials can be made non-magnetic at selected locations, but thesematerials can have relatively low mechanical strength (e.g., no greaterthan 80 ksi). This lower strength may result in damage or destruction ofthe posts in some machines. Conversely, using the non-ferromagneticposts described herein can reduce flux leakage while providing a greatermechanical strength (e.g., greater than 80 ksi and up to 200 ksi ormore).

FIG. 1 illustrates one example of an electric machine assembly 100. Theelectric machine 100 can be a synchronous reluctance and interiorpermanent magnet machine. The electric machine 100 includes a stator 102having distributed or concentrated conductive windings 104 through whichelectric current is conducted to cause the electric machine 100 tooperate. The electric machine 100 also includes a rotor 106 formed froma laminated stack of conductive sheets (e.g., steel sheets), insulatedfrom each other and clamped together. The machine assembly 100 canoperate as a motor that operates to propel a vehicle. For example, therotor 106 can be rotated by the electric current in the windings 104 ofthe stator 102, which rotates a shaft joined to the rotor 106. Thisshaft can be coupled with turbine blades, axles, wheels, or the like, tohelp propel a vehicle such as an airplane, land-based vehicle (e.g.,automobile, rail vehicle, mining vehicle, etc.), or marine vessel.

The rotor 106 is formed from a ferromagnetic material that allowsmagnetic flux to flow through the rotor 106. The rotor 106 includesseveral features that define magnetic flux carrier portions 108 of therotor 106 and magnetic flux barriers 110 of the rotor 106. The fluxbarriers 110 are portions of the rotor 106 that have been removed, suchas air gaps in the rotor 106. Permanent magnets 112 can be placed insidethese flux barriers 110. Alternatively, no magnets 112 are in the fluxbarriers 110. The flux carrier portions 108 represent segments of therotor 106 that remain after the flux barriers 110 are cut from, removed,or otherwise formed in the rotor 106.

Neighboring flux carrier portions 108 are connected by elongatedferromagnetic posts 114 along radial directions (e.g., directions thatradially extend from a center axis or axis of rotation 116 of the rotor106). The ends of the flux carrier portions 108 are connected byelongated bridges 118 along circumferential directions (e.g., directionsthat circumferentially surround the axis of rotation 116 of the rotor106). The flux carrier portions 108 and/or bridges 118 can be formedwhen the flux barriers 110 are cut from the sheets forming the rotor106.

In operation, a varying electric current is conducted through thewindings 104 to cause the rotor 106 to rotate relative to the stator102. This current creates magnetic flux in the rotor 106. The fluxcarrier portions 108 guide and carry magnetic flux in the rotor 106while the barrier portions 110 block or impede flow of the magnetic fluxin the rotor 106. These portions 108, 110 create a larger reluctancepath in the rotor 106 along a first axis 120 (e.g., the quadrature or‘q’ axis of the rotor 106) and a smaller reluctance path in the rotor106 along a different, second axis 122 (e.g., the direct or ‘d’ axis ofthe rotor 106). The difference in reluctance along the different axes120, 122 leads to an overall reluctance torque. The difference inreluctance can be created by the shape and size of the flux carrierportions 108 and the flux barrier portions 110.

One problem with the rotor 106 is that a significant amount of magneticflux can leak of the lower reluctance path along the axis 120 at theposts 114. The leaking flux in the posts 114 reduces the power factor ofthe rotor 106, reduces the torque density of the rotor 106, and canrequire more current to be conducted through the windings 104 togenerate the same amount of torque (as a rotor 106 that does not have asmuch flux leakage at the posts 114).

FIG. 2 illustrates one example of a segment of a rotor 206 having fluxcarrier portions 208 and flux barrier portions 210. The rotor 206 can besimilar to the rotor 106 shown in FIG. 1, except that the shape andnumber of the portions 208, 210 may differ from the portions 108, 110shown in FIG. 1. Permanent magnets 232 can be inserted in the barrierportions 210, as described above. A post 214 connects neighboring fluxcarrier portions 208, as described above.

One option to reduce the flux leakage at the posts 114, 214 in therotors 106, 206 is to remove the posts 114, 214. FIG. 3 illustrates oneembodiment of a segment of a rotor 306 having the flux carrier portions208 and the flux barrier portions 210 shown in FIG. 2. The rotor 306 canbe similar to the rotors 106, 206, except that the posts 114, 214 in therotors 106, 206 are removed in the rotor 306. Instead, an airgap 324 isleft in the space where the post 214 is located in the rotor 206.

Removing the ferromagnetic post 114, 214 from the rotors 106, 206 canreduce the leakage of magnetic flux along the q-axes 120 in the rotors106, 206. FIG. 4 illustrates examples of airgap torques 426, 428 thatare generated by rotation of the rotors 206, 306 with and without theferromagnetic posts 214, respectively. The torques 426, 428 representthe amount of torque generated by rotation of the rotors 206, 306 uponapplication of the same electric current to the conductive windings 104in the stator 102 (shown in FIG. 1). The torques 426, 428 are shownalongside a horizontal axis 430 representative of positions of therotors 206, 306 and alongside a vertical axis 432 representative oftorques generated by the rotors 206, 306. As shown, the torques 428generated by the rotors 306 that do not include the ferromagnetic posts114, 214 are significantly greater than the torques 426 generated by therotors 106, 206 that include the ferromagnetic posts 114, 214. Forexample, removing the ferromagnetic posts 114, 214 can increase thetorque generated by rotation of the rotor by an average of 13% acrossall rotor positions.

In one embodiment, an electric machine assembly 100 includes the stator102 and the rotor 306 having the airgap 324 in place of the posts 114,214. The airgap 324 can be a space or void that does not include anyferromagnetic material and can be referred to as a non-magnetic space orvoid. The airgap 324 can be bounded by the permanent magnets 323 on bothcircumferential sides of the airgap 324 (e.g., the opposite sides of theairgap 324 that are along a circumferential direction relative to therotation axis 116) and can be bounded by the flux carrier portions 208of the rotor 306 in both radial sides of the airgap 324 (e.g., theopposite sides of the airgap 324 that are along a direction thatradially extends away from the rotation axis 116). Removal or theabsence of the posts 114, 214 can significantly reduce the leakage ofmagnetic flux from the flux carrier portions 208 of the rotor 306, andtherefore can significantly increase the torque or torque densitygenerated by the assembly 100 (and/or reduce the amount of currentneeded to produce the same torque as an assembly that includes the posts114, 214).

But, removing the posts 114, 214 can pose mechanical problems foroperation of the assembly 100. The posts 114, 214 provide structuralsupport for the flux carrier portions 208. Removing the posts 114, 214to leave an empty airgap 324 can, in some embodiments, result instructural damage or failure to the rotor 306 due to the high speeds atwhich the rotor 306 rotates. In another embodiment, the airgap 324 isfilled or replaced with a non-magnetic post that both reduces leakage ofmagnetic flux from the flux carrier portions 208 (as the airgap 324does) and provides structural support to the flux carrier portions 208to prevent mechanical failure of the portions 208 (which the airgap 324may not do).

FIG. 5 illustrates a front view of a rotor 506 of the electric machineassembly 100 shown in FIG. 1 according to another embodiment. FIG. 6illustrates a perspective cut-away view of the segment of the rotor 506shown in FIG. 5 according to one embodiment. FIG. 7 illustrates across-sectional cut-away view of the segment of the rotor 506. The rotor506 includes the flux carrier portions 208 and flux barrier portions 210described above. The magnets 232 can be inserted in the barrier portions210. The rotor 506 is coupled with a shaft 552 that is rotated by therotor 506 during operation of the assembly 100.

The rotor 506 optionally can include airgaps (not shown) between themagnets 232 along circumferential directions 534 and located betweenneighboring flux carrier portions 208 along a radial direction 536. Thecircumferential directions 534 encircle the rotation axis 116 (shown inFIG. 1) of the rotor 506. The radial direction 536 radially extends awayfrom the rotation axis 116. These airgaps can be at least partiallyfilled by a non-magnetic post 538.

The post 538 provides structural support to the flux carrier portions208 while reducing (or not increasing) the leakage of flux from the fluxcarrier portions 208. The post 538 is a non-magnetic ornon-ferromagnetic body formed from one or more materials that are notferromagnetic materials in one embodiment. For example, the post 538 canbe formed from one or more of aluminum, non-ferromagnetic stainlesssteel, titanium, copper beryllium, or any other non-magnetic metal,ceramic, composite material (e.g., such as carbon fiber or alloys), etc.Optionally, the non-magnetic post 538 can be made of an insulating,non-metallic material or a high strength alloy that is electricallynon-conductive. The post 538 can be formed from thinner sections orplates 740 (shown in FIG. 7) that are coupled together (e.g., byinterlocking, press-fitting, lamination, etc.). These sections or plates740 can be insulated from each other by including a dielectric layerbetween neighboring sections or plates 740. Alternatively, the post 538can be formed as a single and/or homogeneous body that is not formed bycoupling multiple parts together.

The posts 538 are elongated in the radial directions 536 from one fluxcarrier portion 208 to another flux carrier portion 208, with thesecarrier portions 208 being on opposite sides of the same flux barrierportion 210. The posts 538 also are elongated along the direct axes 120of the rotors 506. Each of the posts 538 is positioned as a bridgebetween the carrier portions 208 that are on opposite sides of the samebarrier portion 210, even though the posts 538 do not carry magneticflux. For example, the magnetic flux flowing in the carrier portions 208does not flow through the posts 538 coupling the carrier portions 208with each other. Instead, the magnetic flux flows or is carried throughthe carrier portions 208 and predominantly along the quadrature axes 122of the assemblies 100 due to the quadrature axes 122 providing lowerreluctance paths to the flow of the magnetic flux in the rotors 506relative to the paths along the direct axes 120 (that extend through theposts 538 along the lengths of the posts 538) of the assemblies 100.

The illustrated posts 538 have opposite ends 642, 644 (labeled in FIG.6) that are joined by an elongated center body 646 (labeled in FIG. 6).The ends 642, 644 can be wider than the center body 646. For example, anouter width dimension 648 (labeled in FIG. 6) of each of the ends 642,644 can be larger than an outer width dimension 650 (labeled in FIG. 6)in the middle (along the length) of the center body 646. The widthdimensions 648, 650 can be measured in the circumferential directions534 or directions that are parallel to the circumferential directions534 (e.g., curved directions that do not intersect the circumferentialdirections). Alternatively, the width dimensions 648, 650 can bemeasured in directions that are perpendicular to the radial direction536 and that are in the plane defined by the rotor 506 shown in FIG. 6.

The post 538 shown in FIGS. 5 through 7 has a dog bone shape, butalternatively can have another shape. For example, the post 538 can havea dumbbell shape with a steeper transition between the center body 646and the ends 642, 644, the post 538 can have a fluted shape with a moregradual transition between the center body 646 and the ends 642, 644,the post 638 can have triangle-shaped ends 642, 644, the post 638 canhave dovetail shapes at the ends 642, 644, or the post 638 can haveanother shape that is able to interlock carrier portions with eachother.

FIG. 8 illustrates a front view of a segment of another embodiment of arotor 806 of the assembly 100. The rotor 806 includes the flux carrierportions 208, flux barrier portions 210, magnets 232, and posts 538described above. The rotor 806 also is coupled with the shaft 552described above. The rotor 806 can be a composite rotor that is formedfrom an assembly 854 of laminated ferromagnetic portions or layers (withthe layers being planar and parallel to the plane of FIG. 8) that areshrink-fitted onto a solid ferromagnetic body 856. This shrink fittingcan be performed by creating the laminated portion assembly 854 inlarger dimensions that shrink during heating or operation of the rotor806. This shrinking can reduce the dimensions of the assembly 854 todimensions that couple and secure the assembly 854 to the body 856.Alternatively, a dove tail or other interlocking mechanism can be usedto couple the laminated assembly 854 with the solid body 856. In oneembodiment, the rotor is formed by coupling the laminated layers of theassembly 854 with the solid body 856 using the posts 538. The laminatedassembly 854 is coupled with the solid body 856 at an interface 858. Theposts 538 can then be axially slid or otherwise inserted into theairgaps 524. This manufacturing technique can enable the separateportions of the laminated assembly 854, which experience greaterelectromagnetic losses (e.g., flux leakage), to be laminated together,while other portions that do not experience as much electromagneticlosses to be solid bodies (and thereby easier to forge or machine). Inanother embodiment, the non-magnetic post 538 can be a part/extension ofthe shaft 552 (made of same material as 538) wherein the non-magneticassembly can be axially inserted into the preformed cuts on laminatedferromagnetic portion 854 and solid ferromagnetic portion 856.Alternatively, the posts 538 can be additively manufactured. Forexample, three-dimensional printing can be used to print the posts inthe airgaps of the rotor so that the posts are formed within the rotorand are not formed before placing the posts in the airgaps of the rotor.

In one embodiment, the rotor 506, 806 shown in FIGS. 5 through 8 caninclude one or more stress relief features. These relief features caninclude small cut outs or extensions of the airgap 524 into which thepost 538 is inserted. For example, each stress relief features can be anarch-shaped cutout or removal of the rotor 506, 806 that axially extendsthrough the layers of the rotor 506, 806. The relief features can belocated radially inward and outward of the post 538. For example, onerelief feature can be located between the rotation axis 116 of the rotor506, 806 and the post 538 along the radial direction 536, while anotherrelief feature can be located between the post 538 and the stator 102along the radial direction 536. Adding the relief features to the rotor506, 806 can significantly reduce the mechanical stress imparted on orexperienced by the rotor 506, 806 at interfaces between the rotor 506,806 and the post 538 on both sides of the radial direction 536. Forexample, adding the relief features to the rotor 506, 806 can reduce themaximum principal stress exerted on the rotor 506, 806 at interfacesbetween the rotor 506, 806 and the post 538 on both sides of the radialdirection 536 by at least one order of magnitude. In one embodiment,addition of the relief features reduces the maximum principal stress byat least 14%.

FIG. 10 illustrates another embodiment of a rotor 1006 of the electricmachine assembly 100 shown in FIG. 1 according to another embodiment.The rotor 1006 includes the flux carrier portions 208 and the fluxbarrier portions 210 described above. One difference between the rotor1006 and other rotors shown and/or described herein is the presence ofone or more posts 214 within the flux barrier portions 210 and multiple,separate magnets 232 in one or more of the flux barrier portions 210. Asshown in FIG. 10, posts 214 can radially extend through a flux barrierportion 210 to subdivide the flux barrier portion 210 into multiple,separate chambers. Separate magnets 232 can be inserted into two or moreof these chambers defined by the posts 214, also as shown in FIG. 10.Optionally, a flux barrier portion 210 can be divided into a differentnumber of separate chambers by a different number of posts 214 and/or adifferent number of magnets 232 can be inserted into the same fluxbarrier portion 210.

FIG. 9 illustrates a flowchart of one embodiment of a method 900 formanufacturing a rotor of an electric machine assembly. The method 900can be used to create one or more of the rotors 506, 806 describedherein. At 902, several magnetically conductive sheets are obtained.These sheets can be conductive such that magnetic flux is able to flowthrough the sheets. The sheets can be cut into the shape of the rotor(e.g., into circles).

At 904, elongated magnetic flux carrier portions are formed into themagnetically conductive sheets. These carrier portions 208 can be formedby cutting elongated magnetic flux barriers 210 into the conductivesheets. The barriers 210 can be cut into the conductive sheets such thatthe magnetic flux barriers 210 are separated from each other in radialdirections 536 of the conductive sheets. The conductive sheets can belaminated together prior to or after forming the carrier portions.

At 906, non-magnetic posts are inserted into the magnetic flux barriers.For example, the posts 538 can be inserted into airgaps 524 formed bythe flux barriers 210. The airgaps 524 can be oriented such that each ofthe non-magnetic posts 538 is elongated in a different radial direction536 outward from the rotation axis 116 of the rotor 506, 806. The posts538 are inserted into the airgaps 524 such that the posts 538 extendfrom one magnetic flux carrier portion 208 to another magnetic fluxcarrier portion 208 on opposite sides the magnetic flux barrier 210.

At 908, the rotor is formed using the conductive sheets having themagnetic flux carrier portions, the non-magnetic posts, and the magneticflux barriers. For example, the rotor 506, 806 can be inserted into thestator 102. Optionally, the rotor 506, 806 can be formed by combining alaminate assembly 854 of the conductive sheets with a solid body 856 offerromagnetic material at an interface 858 that extends through theairgaps 524 and the posts 538.

In one embodiment, an electric machine assembly includes a rotor formedfrom one or more conductive sheets having elongated magnetic fluxbarriers separated from each other in radial directions that radiallyextend away from an axis of rotation of the rotor. The magnetic fluxbarriers are separated from each other by magnetic flux carrier portionsof the one or more conductive sheets. The assembly also includes anon-magnetic post coupled with the magnetic flux carrier portions of theone or more conductive sheets on opposite sides of at least one of themagnetic flux barriers. The non-magnetic post is elongated in the radialdirections from a first magnetic flux carrier portion to a secondmagnetic flux carrier portion of the magnetic flux carrier portions onthe opposite sides of the at least one magnetic flux barrier.

Optionally, the non-magnetic post reduces magnetic flux leakage from theone or more conductive sheets such that a torque generated by operationof the rotor is increased relative to another rotor that does notinclude the non-magnetic post at the same rotor speed and statorexcitation.

Optionally, the non-magnetic post is elongated along a direct axis ofthe rotor having a greater reluctance than a quadrature axis of therotor.

Optionally, the non-magnetic post is formed from one or more ofaluminum, non-ferromagnetic steel, titanium, copper beryllium, anothernon-ferromagnetic metal material, a ceramic material, a compositematerial (such as but not limited to carbon fiber), an alloy, or anyother non-magnetic material.

Optionally, the non-magnetic post is formed from an electricallyinsulating material.

Optionally, the non-magnetic post includes opposite ends joined by anelongated center body. The opposite ends can have larger widthdimensions in directions that are transverse to the radial directionsthan a width dimension of the center body in the directions that aretransverse to the radial direction.

Optionally, the non-magnetic post has a dog bone shape, a dumbbellshape, an hourglass shape, a dovetail shape, or any other shape capableof having interlocking mechanisms between parts of the rotor.

Optionally, the assembly also includes one or more magnets disposed inthe magnetic flux barriers.

In one embodiment, a rotor of an electric machine assembly includesplural magnetically conductive sheets laminated with each other. Theconductive sheets have elongated magnetic flux barriers separated fromeach other in radial directions that radially extend away from an axisof rotation of the rotor. The magnetic flux barriers are separated fromeach other by magnetic flux carrier portions of the one or moreconductive sheets. The rotor also includes multiple non-magnetic postswhich are laminated, insulated and coupled with the magnetic fluxcarrier portions of the one or more conductive sheets on opposite sidesof at least one of the magnetic flux barriers. The non-magnetic postsare elongated in the radial directions from a first magnetic fluxcarrier portion to a second magnetic flux carrier portion of themagnetic flux carrier portions on the opposite sides of each of themagnetic flux barriers.

Optionally, the non-magnetic posts reduce magnetic flux leakage from theone or more conductive sheets such that a torque generated by operationof the electric motor assembly is increased relative to another electricmotor assembly that does not include the non-magnetic posts at the samerotor speed and stator excitation.

Optionally, at least one of the non-magnetic posts is elongated along adirect axis of the conductive sheets having a greater reluctance than aquadrature axis of the conductive sheets.

Optionally, the non-magnetic posts are formed from one or more ofaluminum, non-ferromagnetic steel, titanium, copper-beryllium, anothernon-ferromagnetic metal, a ceramic, a composite material (such as butnot limited to carbon fiber).

Optionally, the non-magnetic posts are formed from an electricallyinsulative material.

Optionally, each of the non-magnetic posts includes opposite ends joinedby an elongated center body. The opposite ends can have larger widthdimensions in directions that are transverse to the radial directionsthan a width dimension of the center body in the directions that aretransverse to the radial direction.

Optionally, each of the non-magnetic posts has a dog bone shape,dumbbell shape, hour-glass shape, dovetail shape, or another suitableshape capable of having interlocking mechanisms between the parts of therotor.

Optionally, the rotor also includes one or more magnets disposed in themagnetic flux barriers.

In one embodiment, a method includes obtaining magnetically conductivesheets and forming elongated magnetic flux carrier portions of theconductive sheets by cutting elongated magnetic flux barriers into theconductive sheets. The magnetic flux barriers are cut into theconductive sheets such that the magnetic flux barriers are separatedfrom each other in radial directions of the conductive sheets. Themethod also includes inserting or forming non-magnetic posts into themagnetic flux barriers such that each of the non-magnetic post iselongated in a different radial direction of the radial directions froma first magnetic flux carrier portion to a second magnetic flux carrierportion of the magnetic flux carrier portions on opposite sides of atleast one magnetic flux barrier, and forming at least part of a rotorfor an electric machine assembly using the conductive sheets having themagnetic flux carrier portions, the non-magnetic posts, and the magneticflux barriers.

Optionally, inserting the non-magnetic posts reduces magnetic fluxleakage from the rotor such that a torque generated by operation of therotor is increased relative to another rotor that does not include thenon-magnetic post at the same rotor speed and stator excitation.

Optionally, the non-magnetic posts are inserted into the magnetic fluxbarriers such that at least one of the non-magnetic posts is elongatedalong a direct axis of the rotor having a greater reluctance than aquadrature axis of the rotor.

Optionally, forming the magnetic flux carrier portions includes cuttingelongated openings that are oriented along the radial directions of theconductive sheets, the elongated openings having wider opposite endholes joined by a thinner elongated slot.

Optionally, inserting the non-magnetic posts into the magnetic fluxbarriers includes inserting wider opposite ends of the non-magneticposts into the wider opposite end holes of the elongated openings andelongated center bodies of the non-magnetic posts into the elongatedslot.

Optionally, the method also includes inserting magnets into the magneticflux barriers.

Optionally, forming at least part of the rotor includes fixing apreformed laminated section of the rotor to a solid body of the rotorusing one or more of shrink-fitting or the posts.

It is to be understood that the above description is intended to beillustrative, and not restrictive. For example, the above-describedembodiments (and/or aspects thereof) may be used in combination witheach other. In addition, many modifications may be made to adapt aparticular situation or material to the teachings of the inventivesubject matter without departing from its scope. While the dimensionsand types of materials described herein are intended to define theparameters of the inventive subject matter, they are by no meanslimiting and are exemplary embodiments. Many other embodiments will beapparent to one of ordinary skill in the art upon reviewing the abovedescription. The scope of the inventive subject matter should,therefore, be determined with reference to the appended claims, alongwith the full scope of equivalents to which such claims are entitled. Inthe appended claims, the terms “including” and “in which” are used asthe plain-English equivalents of the respective terms “comprising” and“wherein.” Moreover, in the following claims, the terms “first,”“second,” and “third,” etc. are used merely as labels, and are notintended to impose numerical requirements on their objects. Further, thelimitations of the following claims are not written inmeans-plus-function format and are not intended to be interpreted basedon 35 U.S.C. § 112(f), unless and until such claim limitations expresslyuse the phrase “means for” followed by a statement of function void offurther structure.

This written description uses examples to disclose several embodimentsof the inventive subject matter, and also to enable one of ordinaryskill in the art to practice the embodiments of inventive subjectmatter, including making and using any devices or systems and performingany incorporated methods. The patentable scope of the inventive subjectmatter is defined by the claims, and may include other examples thatoccur to one of ordinary skill in the art. Such other examples areintended to be within the scope of the claims if they have structuralelements that do not differ from the literal language of the claims, orif they include equivalent structural elements with insubstantialdifferences from the literal languages of the claims.

The foregoing description of certain embodiments of the presentinventive subject matter will be better understood when read inconjunction with the appended drawings. The various embodiments are notlimited to the arrangements and instrumentality shown in the drawings.

As used herein, an element or step recited in the singular and proceededwith the word “a” or “an” should be understood as not excluding pluralof said elements or steps, unless such exclusion is explicitly stated.Furthermore, references to “one embodiment” of the present invention arenot intended to be interpreted as excluding the existence of additionalembodiments that also incorporate the recited features. Moreover, unlessexplicitly stated to the contrary, embodiments “comprising,”“comprises,” “including,” “includes,” “having,” or “has” an element or aplurality of elements having a particular property may includeadditional such elements not having that property.

What is claimed is:
 1. An electric machine assembly comprising: a rotorformed from one or more magnetically conductive sheets having elongatedmagnetic flux barriers separated from each other in radial directions,the magnetic flux barriers separated from each other by magnetic fluxcarrier portions of the one or more conductive sheets; and anon-magnetic post coupled with the magnetic flux carrier portions of theone or more magnetically conductive sheets on opposite sides of at leastone of the magnetic flux barriers, the non-magnetic post elongated inthe radial directions from a first magnetic flux carrier portion to asecond magnetic flux carrier portion on the opposite sides of the atleast one magnetic flux barrier; wherein the rotor includes one or morestress relief features, each stress relief feature being an arch-shapedcutout or removal of the rotor that axially extends through the rotor,the one or more stress relief features being located radially inward andoutward of the non-magnetic post.
 2. The electric machine assembly ofclaim 1, wherein the non-magnetic post reduces magnetic flux leakagefrom the one or more magnetically conductive sheets such that a torquegenerated by operation of the rotor is increased relative to anotherrotor that does not include the non-magnetic post at the same rotorspeed and stator excitation.
 3. The electric machine assembly of claim1, wherein the non-magnetic post is elongated along a direct axis of therotor.
 4. The electric machine assembly of claim 1, wherein thenon-magnetic post is formed from one or more of aluminum,non-ferromagnetic steel, titanium, copper beryllium, anothernon-ferromagnetic metal material, a ceramic material, a compositematerial, or an alloy.
 5. The electric machine assembly of claim 1,wherein the non-magnetic post is formed from an electrically insulatingmaterial.
 6. The electric machine assembly of claim 1, wherein thenon-magnetic post includes opposite ends joined by an elongated centerbody, the opposite ends having larger width dimensions in directionsthat are transverse to the radial directions than a width dimension ofthe center body in the directions that are transverse to the radialdirection.
 7. The electric machine assembly of claim 6, wherein thenon-magnetic post has a dog bone, dumbbell, hourglass, or dovetailshape.
 8. The electric machine assembly of claim 1, further comprisingone or more magnets disposed in the magnetic flux barriers.
 9. A rotorof an electric machine assembly, the rotor comprising: pluralmagnetically conductive sheets laminated with each other, themagnetically conductive sheets having elongated magnetic flux barriersseparated from each other in radial directions, the magnetic fluxbarriers separated from each other by magnetic flux carrier portions ofthe magnetically conductive sheets; and multiple non-magnetic postswhich are laminated, insulated and coupled with the magnetic fluxcarrier portions of the magnetically conductive sheets on opposite sidesof at least one of the magnetic flux barriers, the non-magnetic postselongated in the radial directions from a first magnetic flux carrierportion to a second magnetic flux carrier portion on the opposite sidesof each of the magnetic flux barriers; wherein the rotor includes one ormore stress relief features, each stress relief feature being anarch-shaped cutout or removal of the rotor that axially extends throughthe rotor, the one or more stress relief features being located radiallyinward and outward of the non-magnetic post.
 10. The rotor of claim 9,wherein the non-magnetic posts reduce magnetic flux leakage from the oneor more magnetically conductive sheets such that a torque generated byoperation of the electric machine assembly is increased relative toanother electric machine assembly that does not include the non-magneticposts at the same rotor speed and stator excitation.
 11. The rotor ofclaim 9, wherein at least one of the non-magnetic posts is elongatedalong a direct axis of the magnetically conductive sheets.
 12. The rotorof claim 9, wherein the non-magnetic post is formed from one or more ofaluminum, non-ferromagnetic steel, titanium, copper-beryllium, anothernon-ferromagnetic metal, a ceramic, or a composite material.
 13. Therotor of claim 9, wherein the non-magnetic posts are formed from anelectrically insulating material.
 14. The rotor of claim 9, wherein eachof the non-magnetic posts includes opposite ends joined by an elongatedcenter body, the opposite ends having larger width dimensions indirections that are transverse to the radial directions than a widthdimension of the center body in the directions that are transverse tothe radial direction.
 15. The rotor of claim 14, wherein each of thenon-magnetic posts has a dog bone, dumbbell, hour-glass, or dovetailshape.
 16. The rotor of claim 9, further comprising one or more magnetsdisposed in the magnetic flux barriers.